Adding ConsumerResource and ConsumerPool for ConsumeKafka

Signed-off-by: joewitt <joewitt@apache.org>

nifi-nar-bundles/nifi-kafka-bundle/nifi-kafka-pubsub-processors/src/main/java/org/apache/nifi/processors/kafka/pubsub/ConsumerPool.java

@@ -0,0 +1,148 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.nifi.processors.kafka.pubsub;
+
+import org.apache.kafka.clients.consumer.Consumer;
+import org.apache.kafka.clients.consumer.KafkaConsumer;
+import org.apache.nifi.logging.ComponentLog;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.util.Collections;
+import java.util.Properties;
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.LinkedBlockingQueue;
+
+/**
+ * A pool of Kafka Consumers for a given topic. Clients must create the ConsumerPool and call initialize() before
+ * acquiring consumers. Consumers should be returned by calling returnConsumerResource.
+ */
+public class ConsumerPool implements Closeable {
+
+    private final int size;
+    private final BlockingQueue<ConsumerResource> consumers;
+    private final String topic;
+    private final Properties kafkaProperties;
+    private final ComponentLog logger;
+    private boolean initialized = false;
+
+    /**
+     * Initializes the pool with the given size, topic, properties, and logger, but does not create any consumers until initialize() is called.
+     *
+     * @param size the number of consumers to pool
+     * @param topic the topic to consume from
+     * @param kafkaProperties the properties for each consumer
+     * @param logger the logger to report any errors/warnings
+     */
+    public ConsumerPool(final int size, final String topic, final Properties kafkaProperties, final ComponentLog logger) {
+        this.size = size;
+        this.logger = logger;
+        this.topic = topic;
+        this.kafkaProperties = kafkaProperties;
+        this.consumers = new LinkedBlockingQueue<>(size);
+    }
+
+    /**
+     * Creates the consumers and subscribes them to the given topic. This method must be called before
+     * acquiring any consumers.
+     */
+    public synchronized void initialize() {
+        if (initialized) {
+            return;
+        }
+
+        for (int i=0; i < size; i++) {
+            ConsumerResource resource = createConsumerResource();
+            consumers.offer(resource);
+        }
+
+        initialized = true;
+    }
+
+    /**
+     * @return a ConsumerResource from the pool, or a newly created ConsumerResource if none were available in the pool
+     * @throws IllegalStateException if attempting to get a consumer before calling initialize()
+     */
+    public synchronized ConsumerResource getConsumerResource() {
+        if (!initialized) {
+            throw new IllegalStateException("ConsumerPool must be initialized before acquiring consumers");
+        }
+
+        ConsumerResource consumerResource = consumers.poll();
+        if (consumerResource == null) {
+            consumerResource = createConsumerResource();
+        }
+        return consumerResource;
+    }
+
+    /**
+     * If the given ConsumerResource has been poisoned then it is closed and not returned to the pool,
+     * otherwise it is attempted to be returned to the pool. If the pool is already full then it is closed
+     * and not returned.
+     *
+     * @param consumerResource
+     */
+    public synchronized void returnConsumerResource(final ConsumerResource consumerResource) {
+        if (consumerResource == null) {
+            return;
+        }
+
+        if (consumerResource.isPoisoned()) {
+            closeConsumer(consumerResource.getConsumer());
+        } else {
+            boolean added = consumers.offer(consumerResource);
+            if (!added) {
+                closeConsumer(consumerResource.getConsumer());
+            }
+        }
+    }
+
+    /**
+     * Closes all ConsumerResources in the pool and resets the initialization state of this pool.
+     *
+     * @throws IOException should never throw
+     */
+    @Override
+    public synchronized void close() throws IOException {
+        ConsumerResource consumerResource;
+        while ((consumerResource = consumers.poll()) != null) {
+            closeConsumer(consumerResource.getConsumer());
+        }
+        initialized = false;
+    }
+
+    private ConsumerResource createConsumerResource() {
+        final Consumer<byte[],byte[]> kafkaConsumer = new KafkaConsumer<>(kafkaProperties);
+        kafkaConsumer.subscribe(Collections.singletonList(this.topic));
+        return new ConsumerResource(kafkaConsumer, this, logger);
+    }
+
+    private void closeConsumer(Consumer consumer) {
+        try {
+            consumer.unsubscribe();
+        } catch (Exception e) {
+            logger.warn("Failed while unsubscribing " + consumer, e);
+        }
+
+        try {
+            consumer.close();
+        } catch (Exception e) {
+            logger.warn("Failed while closing " + consumer, e);
+        }
+    }
+
+}

nifi-nar-bundles/nifi-kafka-bundle/nifi-kafka-pubsub-processors/src/main/java/org/apache/nifi/processors/kafka/pubsub/ConsumerResource.java

@@ -0,0 +1,76 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.nifi.processors.kafka.pubsub;
+
+import org.apache.kafka.clients.consumer.Consumer;
+import org.apache.kafka.clients.consumer.ConsumerRecords;
+import org.apache.nifi.logging.ComponentLog;
+
+import java.io.Closeable;
+import java.io.IOException;
+
+/**
+ * A wrapper for a Kafka Consumer obtained from a ConsumerPool. Client's should call poison() to indicate that this
+ * consumer should no longer be used by other clients, and should always call close(). Calling close() will pass
+ * this consumer back to the pool and the pool will determine the appropriate handling based on whether the consumer
+ * has been poisoned and whether the pool is already full.
+ */
+public class ConsumerResource implements Closeable {
+
+    private final ComponentLog logger;
+    private final Consumer<byte[],byte[]> consumer;
+    private final ConsumerPool consumerPool;
+    private boolean poisoned = false;
+
+    /**
+     * @param consumer the Kafka Consumer
+     * @param consumerPool the ConsumerPool this ConsumerResource was obtained from
+     * @param logger the logger to report any errors/warnings
+     */
+    public ConsumerResource(Consumer<byte[], byte[]> consumer, ConsumerPool consumerPool, ComponentLog logger) {
+        this.logger = logger;
+        this.consumer = consumer;
+        this.consumerPool = consumerPool;
+    }
+
+    /**
+     * @return the Kafka Consumer for this
+     */
+    public Consumer<byte[],byte[]> getConsumer() {
+        return consumer;
+    }
+
+    /**
+     * Sets the poison flag for this consumer to true.
+     */
+    public void poison() {
+        poisoned = true;
+    }
+
+    /**
+     * @return true if this consumer has been poisoned, false otherwise
+     */
+    public boolean isPoisoned() {
+        return poisoned;
+    }
+
+    @Override
+    public void close() throws IOException {
+        consumerPool.returnConsumerResource(this);
+    }
+
+}